Pressure cylinder for direct plate printing machines

ABSTRACT

A pressure cylinder for a direct plate printing machine comprises a steel cylinder having a peripheral coating of plastic material. The coating has a total thickness of 0.4 mm to 1 mm and comprises an outer layer of polyurethane having a thickness of about 2 mm and a hardness of Shore D 40* to D 60* and at least one inner layer of polyurethane having a hardness of Shore D 80* to D 90*.

United States Patent 1 [151 3,691,949 [451 Sept. 19, 1972 [21] Appl. No.: 84,446

[30] Foreign Application Priority Data Oct. 27, 1969 Switzerland ..15973/69 [52] US. Cl. ..101/216, 29/130, 101/379,

[51] Int. Cl. B411 29/04 [58] Field 01 Search .....29/l30, 132; 101/348, 401.1, 101/415.1, 379, 216; 161/401 [56] References Cited UNITED STATES PATENTS 3,139,826 7/1964 Rainwater ..101/348 2,248,191 Pratt ......29/130 x 2,997,406 8/ 1961 Freeman et a1 ..29/130 X 3,002,866 10/1961 Gartrell et al ..29/ 132 X 3,147,698 9/ 1964 Ross ..29/132 X 2,741,297 4/1956 Vamuaketis ..ll/40l.1 X 3,053,718 9/1962 l'lechtman et a1...101/4l5.l X 3,085,507 4/1963 Kunetka 101/3 79 3,592,134 7/1971 Paterson ..l0l/269 2,374,194 4/1945 Grupe ..29/130 X FORElGN PATENTS OR APPLICATIONS 662,180 12/1951 Great Britain.....- ..101/379 Primary Examiner-Clyde 1. Coughenour Attorney-Robert E. Burns and Emmanuel J. Lobato [57] ABSTRACT A pressure cylinder for a direct plate printing machine comprises a steel cylinder having a peripheral coating of plastic material. The coating has a total thickness of 0.4 mm to 1 mm and comprises an outer layer of polyurethane having a thickness of about 2 mm and a hardness of Shore D 40 to D and at least one inner layerof polyurethane having a hardness of Shore D to D-9 0.

- 8 Claims, 2 Drawing Figures PRESSURE CYLINDER FOR'DIRECT PLATE 7 PRINTING MACHINES BACKGROUND OF THE INVENTION.

The invention relates to pressure cylinders for direct plate printing machines, the pressure cylinders having a surface layer of non-metallic material.

In direct plate printing machines, a pressure cylinder is provided for pressing paper to be printed, under high pressure, against a rigid inked printing plate or engraved cylinder, in order that a perfect transfer can be made, of color from the engraved lines or grooves on the printing plate or cylinder to the paper. The pressure cylinder is provided with an outer elastic surface layer or cover- The pressure imparted by the pressure cylinder to the paper can be in the order of 1,000 kp for each cm of contact line, that is to say, the line between the periphery of the pressure cylinder and the paper. Consequently, the outer elastic surface layer of the pressure cylinder is submitted, in direct plate printing machines, to a very heavy load, so that the choice of a material for the surface layer is very critical.

Direct plate printing machines are known, which use a pressure cylinder for printing sheets, the outer elastic surface layer of which is made of a material, such as, rubber or English leather or like material having a hardness of about Shore A 98. The life duration of such materials is found to be relatively short, that is to say, a useful life of about 100,000 printings, so that the outer elastic surface layer or cover of the printing drum must be changed very frequently. The cost of frequently changing the outer elastic surface layer is very high.

With some direct plate printing machines, which print with webs, no outer elastic surface layer for the pressure cylinder is used, and therefore the pressure cylinder in such direct plate printing machines is frequently made having a lower metallic surface layer supporting sheet paper layers pressed together under high pressure, for example, 300 kp/cm Such pressure cylinders are often used in direct plate printing machines by national banks. The life duration of such pressure cylinders is, in general, satisfactory, but such pressure cylinders present a lot of drawbacks, for example, the manufacture of such pressure cylinders with layers of compressed paper is very complicated and can be handled only by specialists. The surface layer of the pressure cylinders is generally of a hardness about Shore D 90 and thus harder then necessary for obtain ing an optimal working pressure. Since the layers of compressed paper are pressed again during the printing operation, the pressure applied by the pressure cylinder must frequently be controlled. Moreover, the layers of compressed paper are subjected, because of a very heavy pressure on the whole thickness of the layers, to heating. The thickness of the layers may, for example, be 70 mm. It is therefore not possible to print the reverse side of already printed paper bands with such pressure cylinder, otherwise the printing color would adhere on the surface layer of the pressure cylinder because of the high temperature of the layer of compressed paper.

2 AIMS OF THE INVENTION.

An object of the present invention is to provide a pressure cylinder which substantially avoids the drawbacks of known pressure cylinders for direct plate printing machines and which has a surface layer which can be manufactured in a very easy way, for example, by the user of the printing machine.

A further object of the present invention is the provision of a pressure cylinder, the hardness of the outer surface layer of which allows an optimal pressure to be exerted by the cylinder while at the same time having a life duration longer than that of known surface layers.

According to one aspect of the present invention, a pressure cylinder for a direct plate printing machine, comprising an outer surface layer made of a non-metallic synthetic material, having a hardness between Shore D 20 and D Preferably, the synthetic material can be hardened by heat treatment, and is, for example, a polyurethane.

Preferably, the outer surface layer is composed of a unitary plastics material having a thickness of between 0.2 mm and 1 mm and a hardness between Shore D 50 and D 15.

Alternatively, the thickness of the layer is between 0.4 mm and 1 mm and comprises an external covering layer having a surface hardness of between Shore D 40 and D 60 preferably D 50 and a lower layer beneath the external covering layer having a hardness between Shore D 80 and D both layers of different hardness being made from the same type of synthetic material.

In this way, an external covering layer is provided, giving an optimal pressure, while the material of the lower layer which is of preference mixed with carbon black or carbonate of calcium in a proportion between 5 and 15 percent by weight, gives a higher rigidness for obtaining a good steadiness of the outer surface layer. The whole layer thickness is of preference, in the last embodiment, between 0.4 mm and 1 mm, but it is possible for the thickness to be as little as 0.2 mm.

According to a further aspect of the present invention', a method of making a pressure cylinder for a direct plate printing machine comprises the steps of applying successive layers of a synthetic material to the peripheral surface of a cylinder permitting the layers to harden, binding the layers together and working the outside covering layer to obtain a smooth finish.

Preferably, each layer is applied to the drum in a wet condition, is allowed to dry, and is then provided with a thin cover of binding material before the next layer is applied.

DESCRIPTION OF THE FIGURES OF THE DRAWING.

Embodiments of the invention will now be described, by way of example, reference being made to the Figures of the accompanying drawing in which:

FIG. 1 is a schematic side view of a part of a pressure cylinder according to one embodiment of the invention; and

FIG. 2 is a schematic side view of a part of a pressure cylinder according to a different embodiment of the invention.

, 3 DESCRIPTION OF APREFERRED EMBODIMENT.

As shown in FIG. 1, a pressure cylinder for a'dire'ct plate printing machine comprises a steel cylinder I having on its peripheral surface. an outer surface layer 2. The outer surface layer 2 includes an extemal' covering layer-2a having'a thickness of substantially 0.2 mm and with-carbon'black or calciumzcarbonate in. order to reduce the: flexibility of the lowerlayers. The carbon 759 and a thickness between 0.2 mm and 1' mm.

The pressure cylinder according to the above described embodiments has a life duration which is usually much longer than that of the known pressure cylinders used in sheet printing machines and at least as long as the life of a pressure cylinder provided with a compressed paper layer. The pressure cylinder of the embodiments is simple and cheap to'manufacture and duringoperation is submitted to no compression and no heating, so that, in particular, the backside of paper bands already printed'on the front side, can be printed with the pressure cylinder of theernbodiments.

' In order to manufacture a pressure. cylinder in accordance with the invention, a cylinder for example, of steel, is first degreased with trichloroethylene, mounted in a lathe and then a-thin'layer of a binding material of the material with black carbon or calcium carbonate comprising a proportion between 5 and 15 percent by weight of the mixture. The carbon black and calcium I carbonate act as stiffening materials. A synthetic material of the same type can be used for the covering layer, which includes a plastifier' as one of its constituents, and thereby after hardening as -a hardness between Shore D 40 and D 60, preferably D The thickness of each lower layer is about 0.2 mm and the initial thickness of the covering layer is about 0.4 mm given the fact that duringthe mechanical working of the covering layer an externallayer of about 0.2 mm is removed. In that way, it is ensured that the covering layer of the finished synthetic drum has a thickness of about 0.2 mm. The thickness of various lower layers can also vary between 0.15 mm and 0.3 mm, while, when for the external layer a synthetic material of another composition is chosen, that covering layer must be of about 0.2 mm thicker taking into account the following-mechanical working, that is to say 0.2 mm thicker then the required thickness of that layer.

By providing several relatively thin layers of synthetic material, prejudicial effects by shrinking of synthetic material when hardening are practically having a polyester base is'applied to its peripheral surface, which binding material-is used for a better adhe sion of thefurther layer of elastomers. The binding material is allowed to dry at a slightly elevated temperature for 2 to 3 hours'and then a plurality of layers of asynthetic material having a polyurethane base are applied successively to the cylinder. Eachilayer is about 0.2mm thick and is partiallyhardened before the following layer is applied. The whole thickness of the synthetic material is preferably 0:8 mm. Afterwards the uppersurface of the pressure cylinder is submitted to a synthetic material of the name Volkollan manufactured by the Firm Bayer. In relation to the composition'and applicationof known polyurethane synthetic materials reference can be made for example, to the L'exikon of Hermann RoemPP Francksche Verlagshandlung Stuttgart'fifth'Edition, in particulanto the key words Elastomere on page l,352"Poly,urethane Herstelnamed 1 avoided. Moreover, the providing in several layers-of plastic material have the advantage to give the possibility of choosing for the covering layer a synthetic material of other compositions than that of the underlying or lower layers.

What is claimed is:

1. ha direct'plate printingmachine having an em graved inked plate or cylinder, a pressure cylinder for pressing paper to be printed against said'engraved inked plate or'cylinderunder high pressure, said pressure cylinder comprising a steel cylinder having a peripheral coating of synthetic plastic material, said coating having a-totalthickness of 0.4 mm to 1 mm and comprising an outer layer having a thickness of approximately 0.2 mmand a surface hardness Shore D 40 to D and at least one inner layer having a hardness of Shore D to D said'outer and inner layers being of the same type of plastic material.

2. A pressure cylinder according to claim 1, in which said outer and inner layers are of polyurethane.

3. A pressure cylinder according to claim 2, in which said inner layer contains stiffening material selected from the group consisting of carbon black and calcium carbonate.

4. A pressure cylinder according to claim 3, in which the amount of said stiffening material in said inner layer is between 5 and 15 percent by weight.

5. A pressure cylinder according to claim 1, in whic said outer layer has a smooth surface.

6. A pressure cylinder according to claim 1, in which said coating of plastic material is bonded on sheet steel fixed on the peripheral surface of said steel cylinder.

7. A'pressure cylinder according to claim 1', in which said coating of plasticv material is bonded directly onto said steel cylinder.

8. A pressure cylinder according to claim 1, in which said inner layer has a greater thickness than said outer layer. 

2. A pressure cylinder according to claim 1, in which said outer and inner layers are of polyurethane.
 3. A pressure cylinder according to claim 2, in which said inner layer contains stiffening material selected from the group consisting of carbon black and calcium carbonate.
 4. A pressure cylinder according to claim 3, in which the amount of said stiffening material in said inner layer is between 5 and 15 percent by weight.
 5. A pressure cylinder according to claim 1, in which said outer layer has a smooth surface.
 6. A pressure cylinder according to claim 1, in which said coating of plastic material is bonded on sheet steel fixed on the peripheral surface of said steel cylinder.
 7. A pressure cylinder according to claim 1, in which said coating of plastic material is bonded directly onto said steel cylinder.
 8. A pressure cylinder according to claim 1, in which said inner layer has a greater thickness than said outer layer. 